I would imagine getting textured tiles would give better grip than the smooth tiles, also just take a tape measure and measure the inside of the tank... Put one end on the inside for wall and measure across bending your tape measure at the end of the other wall to get your measurement. Do the same for length and width then multiply the numbers together. That will give you the surface area, it will be in inches. So for example is you have 25" long and 20" wide that will give 500" squared of area. Most boxes of tiles will give coverege in feet so you will need to divide your inch calculation by 12. So if you have 500" squared, divided by 12, you get a total area of 41.66 or 42 feet squared. Will need to make cuts in your tile at some point so a wet saw would be nice to rent if you don't have one already. Also, wood plywood would be a good idea to put down and screw into the bottom of the tank if the tank has only plastic bottom and lay tile on top of the wood. Keep in mind between the plywood, mortar, and tile... This tank will be very heavy to move if need be.